1. Field of the Invention
This invention relates to fluid sampling systems, and more particularly to an automatic water sampling apparatus and method for rapidly and simultaneously collecting a large number of ionic and particulate samples from process streams in boiler systems.
2. Description of the Prior Art
Impurities in water systems exist primarily in two forms, particulate and ionic. In many cases, it is necessary to measure both the level of particulates and the level of ionic species present in water systems. Particulate impurities can be sampled through the use of membrane filters. Depending on the size of the the particles present in the water system, a membrane filter of appropriate pore size is selected. As a sample of the water stream is passed through the membrane filter, the particulate impurities collect on the membrane. During this sampling process, the volume of water passed through the filter is measured. The membrane filter containing the particulate impurities is removed and returned to the laboratory where measurements are made of the amount of particulate impurities present on the membrane. The concentration of the particulate impurities in the water system is then determined by dividing the amount of particulate impurities collected on the membrane by the total water volume throughput.
In a similar manner, ionic impurities can be collected on an ion exchange resin impregnated membrane or in a column of ion exchange resin. As a water sample containing ionic impurities passes through the ion exchange resin impregnated membrane, the ionic impurities are collected on the resin. As with the case of collection of particulate samples, the volume of water passed through the membrane is measured. The membrane is returned to the laboratory where measurements for the amount of ionic impurities are conducted. The concentration of ionic impurities is then determined by dividing the amount of ionic impurities collected on the resin by the total volume throughput.
Frequently these types of sample collection media are used in combination in water sampling systems. This is usually accomplished by first passing the water stream through the membrane filter (to remove particulates) and then immediately through an ion exchange resin impregnated membrane a column of ion exchange resin (to remove ionic impurities). A typical application of such a sampling system is for the collection of corrosion products in condensate/feedwater systems of power plants.
A typical sampling apparatus for the collection of particulate and ionic impurities consists of a sample line connected to a filter holder containing a membrane filter, followed by a second filter holder containing ion exchange resin impregnated membranes. This in turn is connected to either a flowrator (for measurement of flowrate vs. time) or to a flow totalizer (for measurement of total water volume throughput). A bypass line is usually provided upstream of the first filter holder and valves are located in the bypass line immediately upstream of the first filter holder and immediately downstream of the second filter holder. When sampling is to occur, the flow of sample water is initiated through the sample line and out the bypass line of the sample apparatus.
Once the filter holders have been loaded with the appropriate type of membranes, the valves upstream and downstream of the filter holders are opened and the bypass valve is partially closed to provide sample flow through the filter holders. The volume of water passed through the filters is measured using the above flow measuring devices.
Operation of the system is completely manual, however, and the collection of samples must be interrupted each time that the membrane filters require changing. Oftentimes it is desirable to collect membrane samples from several locations in a water system simultaneously over short periods of time, especially during transient conditions. In such situations the use of a manual sampling apparatus, such as that previously described, is not practical. Such an operation would be very labor intensive, as well as very difficult to coordinate, since the particular times at which samples are be obtained, the length of time that a sample is to be collected, and the time interval between samples may be critical to the data desired.
Water sampling systems for ionic impurities are known, e.g. U.S. Pat. No. 4,414,858 (Peterson, et al). This system and others as found in U.S. Pat. Nos. 4,472,354 (Passell, et al) and 4,608,159 (Collins, Jr.) typically also use filters to remove particulates from the sample stream.
It has thus become desirable to develop an apparatus and method capable of collecting membrane samples from several locations in a fluid system simultaneously over short periods of time that does not require a significant amount of manpower and yet provides for sampling capability that can accommodate transient changes of a rapid nature.